A method and a device for controlling a solenoid valve-controlled injection are discussed in DE 43 08 811. Here, the switching point in time of a solenoid valve is determined by evaluating the current flowing through the consumer. For this purpose, discrete value pairs are ascertained for the current and the point in time. The intersection point of two best-fit lines defines the switching point in time of the valve. This intersection point serves as a feature, which characterizes the switching point in time. The point in time, in particular, at which the intersection point lies, serves as the switching point in time.
The ascertained switching point in time is used for controlling the fuel metering.
Solenoid valves for fuel injection in internal combustion engines are normally control-operated. The solenoid valve is referred to below as a valve. The valves are normally an essential component of the injectors, which meter the fuel as a function of the activation of the valves into the combustion chamber or into the intake manifold. Controlled methods are also used in order to compensate for injector-specific differences in the opening behavior and closing behavior of the valves. In these methods, the opening point in time and/or closing point in time of the valve is detected and this point in time or a variable derived therefrom is adjusted to a predefined value.
The open time of the valve may be used as an actual variable or setpoint variable for the adjustment. The open time is the period of time during which the valve is opened. This is calculated based on the activation period for the valve and on the opening delay time and the closing delay time. The opening delay time corresponds to the interval between the activation start and the opening point in time. The closing delay time corresponds to the interval between the end of the activation and the closing point in time.
The determination of the closing point in time and the opening point in time is essential for the adjusted or adapted operation. The point in time at which the valve needle reaches its seat and the fuel flow through the injector is interrupted is referred to as the closing point in time. The point in time at which the valve needle unblocks the fuel flow through the injector is referred to as the opening point in time. The term switching point in time is used below for the terms closing point in time and opening point in time.
The basis for the calculation of the switching point in time is an electrical signal measured after the activation of the valve. In this calculation, the coil voltage present at the valve or the current flowing through the valve may be used, for example. A particular feature, which is ascertained via a suitable detection method, is formed on the measured signal curve at the switching point in time. In the specific embodiment according to the preceding related art, the current curve has a kink.
The detection of the switching point in time exhibits a different quality or definition as a function of the properties of a valve and of the boundary conditions under which the valve is operated. The spring forces, the friction, the magnetic circuit, adhesive forces and additional variables, in particular, determine the properties of the valve. The pressure, the temperature, the media properties such as, for example, the viscosity, the setpoint quantity and additional variables determine the boundary conditions.
The controllers used for adjusting the feature must be configured in such a way that they may achieve the desired setpoint value rapidly, but do not oscillate too severely or become unstable. The design of the controller in this case is always a compromise, since both clear and, therefore, precise switching point in times, as well as weak and, therefore erroneous switching points in time must be expected. If, in the case of a weak, i.e., erroneous switching point in time, a high control amplification is selected, this may result in overshooting or in control instability. Then again however, in the case of a clear switching point in time, a high control amplification is desirable, so that a rapid adjustment is possible.